The IIIA-VA group semi-conductor (semi-conductor formed of IIIA group and VA group elements, such as GaAs, InP or GaP) single crystal substrate is widely used in fields like microwave communication, infrared detection, high-efficiency solar cell, high power laser and LED, and is one of the most important basic group of materials. To meet different application requirements, sometimes there is a need to dope the surface of the single crystal substrate, for example by introducing oxygen in the substrates for subsequent to epitaxial growth for the preparation of pHEMTs (pseudomorphic High Electron Mobility Transistors) and HBTs (Hetero-junction Bipolar Transistors). H. Ch. Alt, Y. V. Gomeniuk and U. Kretzer have discussed the preparation of the oxygen-containing GaAs crystal (cf. the Journal Of Applied Physics, 101, 073516 (2007)), wherein Ga2O3 or As2O3 is added into GaAs charge, and then Liquid-encapsulated Czochralski (Cz) and Vertical Gradient Freeze (VGF) methods are used for growing the crystal, so that oxygen can be introduced into the crystal which has an oxygen concentration of only 0.6-1.1×1016 atoms/cm3. The crystal prepared according to said method has an approximately uniform oxygen distribution; however, the dispersion of oxygen throughout the crystal will inevitably negatively affect the structure of the crystal. Currently, in practical use, the effective part of a crystal substrate is only near the surface within a certain depth, in other words, in order to satisfy practical needs, it is sufficient to merely control the physical and chemical properties of the substrate near surface up to a certain depth. For example, for an oxygen doped crystal substrate, there is no requirement for oxygen content of the inner part thereof, and only the surface part of a certain depth needs to be controlled.
On the other hand, electron mobility of a IIIA-VA group semi-conductor single crystal substrate is an important parameter and is changed generally by doping the semi-conductor materials. Also, if impurities are introduced during single crystal material production, overall integrity of the single crystal material will be adversely affected.
In the present industry, there is a need for a IIIA-VA group semi-conductor single crystal substrate and a method for preparing the same to make the IIIA-VA group semi-conductor single crystal substrate material with a high electron mobility or a high oxygen content within a certain depth from the surface or have both a high electron mobility and a high oxygen content in its surface.